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Old 01-09-2011, 07:01 PM   #1 (permalink)
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Codes P0700,U0100

Does anyone have a fix for these codes, P0700,U0100.? Did a search, but other than loose /chafed wires, not much other info. My `06, completely stock LBZ, is not shifting normal and the check engine light is on. Autozone came up with the 2 codes.
Looking on the bright side, I have over 400,000 miles on 3 Duramax trucks and this is my first Check Engine Light!


2016 DENALI 3500 SRW, LML

2006 Chevrolet 2500HD, LBZ, LS, EXT.CAB LB( work )
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Old 01-09-2011, 08:57 PM   #2 (permalink)
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I have an 2002 and got a check engine light the other day, I also noticed that when I move the shifter from park, slowly all the way down to 2 -- not all the lights indicate correctly and the doors don't lock and unlock correctly after starting, driving, and placing the truck in park.

Using my code scanner (dumb scanner) I found P0700 and P0708 in the history. Internet searches and searching this forum leads me to believe the problem is a faulty NSBU (neutral safety backup switch) on the transmission.

Additionally, I found that a wide variety of symptoms can result to include:

No start condition
Gear shift indicator on dash; flashing, blank, or not following properly (my symptom)
Trans stuck in limp mode or fail safe
DTC's set indicating pressure switch codes
Hard shifting
Slow or No Engagement of Automatic Transmission

The codes associated with a failing NSBU are:

DTC P0708, Neutral start/backup (PNP or NSBU) switch (my code)
DTC P0847, Pressure Switch Manifold (PSM)
DTC P0872, Pressure Switch Manifold (PSM)
DTC P0875, Pressure Switch Manifold (PSM)
DTC P1711, Pressure Switch Manifold (PSM)
DTC P1713, Pressure Switch Manifold (PSM)
DTC U1000, Serial Data Communications (your code)

While out today I stopped at Autozone and Advance Auto and fond the NSBU not in stock, but can be ordered in my area for $180 to $200 depending on who I bought it from.

If you search this forum with the DTC codes P0700 and P0708 you will find all the treads I read and a few "sticky" threads on how to replace the NSBU in less than an hour and no special tools.

The failure of the NSBU is often associated with bad weather, ice, snow, and salt used on roadways. The OEM switches seem to allow moisture, to include salt, into the unit and cause corrosion.

My current challenge is to better understand if I have a 4 speed or a 5 speed Allison as the part numbers for the NSBU are different and the NSBU cost is $35.00 for a 4 speed and $190.00 for the 5 speed -- with my luck I have a 5 speed and will have to empty my wallet for my DMAX AGAIN!!!!!!

Hope this helps you out with your issue,


1998 6.5 Turbo Diesel
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Old 01-09-2011, 10:35 PM   #3 (permalink)
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An 02 2500 will have a 5speed alison in it. Go to an alison dealer for the NSBU switch, IIRC about $70.
2007 GMC Sierra 3500 Classic Dually Loaded SLE Crewcab LBZ Line-X liner Rear DVD Sunroof All on headlights
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2004 GMC Sierra 2500 HD 4X4 Duramax Allison Crewcab No mods. Traded!!!!! I feel for the next owner

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Old 01-10-2011, 07:46 AM   #4 (permalink)
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Thanks MBDmax, I thought all along I had the 5speed, Advance Auto was adimit that I needed to find out as the "electronic" part was non-returnable.

Looking up the nearest Alison dealer now.
1998 6.5 Turbo Diesel
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Old 01-15-2014, 06:51 PM   #5 (permalink)
02 2500hd
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I replaced 3 on my 02, always had shift indicator light "warning" when it was going out.
06 LBZ CCSB Banks Cold air, Banks Cat Back, EGR Delete with "mild" tune. Cat to go next.

Sold it
02 2500HD basically stock, 450k miles now. 5 sets of injectors, valves adjusted, 3rd altinator, 2nd injector pump, 2nd injector modual, 3rd PRNDLL switch, new harmonic ballancer pin, and other work on the moter and trany to keep it going. 3rd transfer case, 2nd frontend. travels down the road at 9300# every day then it gets loaded.

Load it like a Box car, drive it like a Stock car.
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